Deflection yoke with bridge-connected windings

ABSTRACT

A yoke assembly having windings for producing magnetic fields to deflect an electron beam in a predetermined manner. A first and a second set of windings are disposed upon a core for deflecting the electron beam in a vertical and a horizontal sense, respectively. A set of four auxiliary windings is disposed upon the core about points where the horizontal and vertical deflection windings would ordinarily overlap. The auxiliary windings are then connected in series to form a closed, foursided loop or bridge. The bridge is connected in series with both the first and the second set of deflection windings such that the windings of the first set are coupled to opposing nodes of the bridge, and the windings of the second set are coupled to the other, remaining nodes. The effective resistances across the newly-connected first and second sets of windings are substantially decreased while the inductances thereof are virtually unchanged so that the L-R ratios thereof are substantially improved. In one embodiment, the first and second sets of windings are distributed in patterns characterized by relatively low fifthorder and higher harmonics. In still another embodiment, each auxiliary windings has turns of an additional adjacent auxiliary winding interposed intermediate its ends.

United States Patent [1 1 Lister Feb. 12, 1974 DEFLECTION YOKE WITHBRIDGE-CONNECTED WINDINGS [75] Inventor: John W. Lister, Portsmouth, Va.

[73] Assignee: General Electric Company,

Portsmouth, Va.

22 Filed: Dec. 23, 1971 21 Appl. No.: 211,341

Primary ExaminerMaynard R. Wilbur Assistant Examiner-J. M. Potenza 57ABSTRACT A yoke assembly having windings for producing magnetic fieldsto deflect an electron beam in a predetermined manner. A first and asecond set of windings are disposed upon a core for deflecting theelectron beam in a vertical anda horizontal sense, respectively. A setof four auxiliary windings is disposed upon the core about points wherethe horizontal and vertical deflection windings would ordinarilyoverlap. The auxiliary windings are then connected in series to form aclosed, four-sided loop or bridge. The bridge is connected in serieswith both the first and the second set of deflection windings such thatthe windings of the first set are coupled to opposing nodes of thebridge, and the windings of the second set are coupled to the other,remaining nodes. The effective resistances across the newly-connectedfirst and second sets of windings are substantially decreased while theinductances thereof are virtually unchanged so that the LR ratiosthereof are substantially improved.

In one embodiment, the first and second sets of windings are distributedin patterns characterized by relatively low fifth-order and higherharmonics. In still another embodiment, each auxiliary windings hasturns of an additional adjacent auxiliary winding interposedintermediate its ends.

11 Claims, 11 Drawing Figures PATENTEU 3,792,305

sum 1 0F 3 PRIOR ART INVENTOR JOHN W LJSTER BY H \5 ATTORNEY DEFLECTIONYOKE wirii BRIDGE-CONNECTED WINDINGS BACKGROUND OF THE INVENTION Thepresent invention relates to electromagnetic devices and, moreparticularly to improved electromagnetic means for deflecting electronbeams in a cathode ray tube.

In order to produce a display upon the face of a cathode ray tube, it isnecessary to provide means for deflecting an electron beam, or beams,across the face of the tube in a predetermined manner. Various means maybe selected to provide this function and both electrostatic andelectromagnetic means have been successfully utilized for effectingrepeated beam deflection. In cathode ray tube systems utilized fortelevision receivers, however, electromagnetic means are predominentlyused.

A continuing problem which has faced designers of television receiverdeflection systems has been the nonlinearity of the sawtooth-likewaveform which arises in horizontal deflection windings by virtue of theintegration of square-wave voltages applied thereto. While a perfectinductor would produce a linear rise in current, the resistance inherentin actual inductive devices detracts from the operation of thedeflection windings and causes the current rise to be non-linear.

An improved inductance-to-resistance, or L-R, ratio increases theefficiency of deflection windings through reduced 1 R losses, whichresults in a substantially cooler-operating device. The sensitivity ofthe device is also increased, resulting in better system performance. Itwill be appreciated that even when utilizing compensating means incircuit with the deflection windings, the inherent L-R ratio of thedeflection yoke remains substantially unaffected. It will therefore beappreciated that it would be desirable to provide improved deflectionmeans having better linearity characteristics and a superior L-R ratiothan those previously known.

It is therefore an object of the present invention to provide improveddeflection means for a television receiver.

It is a further object to provide a deflection yoke assembly having animproved L-R ratio.

It is another object to provide an improved deflection winding utilizingbridge-connected coils.

It is still another object to provide a toroidal deflection windinghaving an improved L-R ratio and which is readily manufactured.

SUMMARY OF THE INVENTION Briefly stated, in accordance with one aspectof the invention, the foregoing objects are achieved by providing a setof four auxiliary windings upon a core assembly in conjunction with afirst pair of windings which provide vertical deflection, and a secondpair of windings which effect horizontal deflection, of an electronbearn. Each of the four auxiliary windings is a hybird windingconstituted by turns which correspond to what would otherwise beadjacent or overlapping turns of juxtaposed horizontal and verticaldeflection windings. Each of the four auxiliary windings is disposedabout a point on a yoke between a horizontal and a vertical winding. Thefour auxiliary windings are then connected in series to form a closed,four-sided loop which resembles a bridge. Each of the verticaldeflection windings is connected to an opposite corner of the bridge.Each of the horizontal deflection windings is then coupled to one of theremaining, opposite corners or nodes of the bridge. Currents flowingthrough both the horizontal and the vertical deflection windings thustraverse all four of the bridge-connected windings, re sulting in eitheradditive or differential currents therein. The bridge-connected windingsinterposed in the deflection circuits may serve to maintain theeffective inductances thereof, while lowering the series resistance ofeach circuit so that the L-R ratios are markedly improved.Alternatively, smaller wire may be used for the bridge windings. Theincreased resistance of the bridge windings may thus maintain theoriginal L-R ratio, while affording a substantial saving in conductormaterial.

In another embodiment, a yoke winding is disclosed which utilizesbridge-wound turns in combination with vertical and horizontal windingswhich overlap certain of the bridge windings. The distribution of thevertical and horizontal windings provides desirable beam deflectioncharacteristics while facilitating the disposition of turns on the corein a continuous, progressive manner.

In still another embodiment, ones of the turns of each bridge windingare interchanged with corresponding turns of an adjacent bridge winding.The interchanged turns produce additive magnetic flux for deflectioncurrent flowing in a first direction, and bucking magnetic flux fordeflection current flowing in the opposite direction.

BRIEF DESCRIPTION OF THE DRAWINGS While the specification concludes withclaims particularly pointing out and distinctly claiming the subjectmatter which is regarded as the invention, it is believed that theinvention will be better understood from the following description ofthe preferred embodiments taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a schematic drawing of a set of horizontal and verticaldeflection windings as utilized in the prior art;

FIG. 2 is a sectional view of a toroidal coil and core assembly showingthe disposition of various windings upon the core in accordance with theteachings of the prior art;

FIG. 3 is a schematic drawing of an improved deflection winding circuitconstituting one embodiment of the present invention;

FIG. 4 is a cross-sectional diagram showing a developed quadrant of atoroidal yoke core having windings distributed therein;

FIG. 5 is a plot of the distribution of the effective horizontaldeflection winding of FIG. 4;

FIG. 6 is a plot of the distribution of the effective verticaldeflection winding of FIG. 4;

FIG. 7 is a cross-sectional diagram showing another turns placementscheme on a developed quadrant of a toroidal deflection yoke;

FIG. 7a represents a portion of the developed quadrant of FIG. 7 showinga modified turn placement arrangement;

FIG. 8 is a plot of the distribution of the effective horizontaldeflection windings of FIG. 7 and 7a;

FIG. 9 is a plot of the distribution of the effective verticaldeflection windings of FIG. 7 and 7a; and

FIG. is a schematic diagram showing a modified bridge-connecteddeflection circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows, in simplifiedschematic form, a set of windings suitable for deflecting the electronbeam of a cathode ray tube over the viewing screen or face thereof. Apair of vertical windings V, and V are connected in series and coupledacross a source of signals (not shown) which apply a periodic ramp-likeor "sawtooth" current 1,, to the windings. As will be understood bythose skilled in the art, windings V, and V are commonly disposed upon amagnetic core located adjacent the neck of a cathode ray tube. Magneticflux produced by current flowing through vertical windings V, and V isordinarily oriented in a horizontal fashion in order to impart avertical deflection to an electron beam passing therethrough. Similarly,horizontal windings H, and H are connected across another source ofperiodic signals (not shown) for causing a sawtooth current I, to flowtherethrough. Horizontal windings H, and H may advantageously bedisposed upon a common core with vertical windings V, and V anddisplaced 90 therefrom in order to produce a vertical field foreffecting the deflection of an electron beam in a substantiallyhorizontal plane. The junctions of the pairs of horizontal and verticalwindings may advantageously be connected together. Current is applied tothe horizontal windings by means of a balanced source, such as thesecondary winding of a transformer across which the windings arecoupled. Horizontal windings H, and H are thus allowed to float withrespect to ground.

Referring now to FIG. 2, there is shown a simplified cross section of atoroidal core 10 upon which vertical and horizontal deflection windingsare disposed in a manner commonly practiced in the prior art. Verticalwindings V, and V, are placed diametrically opposite one another on theupper and lower halves of core 10., respectively. Similarly, horizontalwindings H, and H, are disposed diametrically opposite one another uponthe core and displaced substantially 90 from the vertical windings. InFIG. 2, as often occurs in the design of such devices, it will be seenthat in order to provide the number of vertical winding turns necesaryfor proper deflection of an electron beam it has been necessary toextend the turns of horizontal windings H, and H so as to overlapportions of vertical windings V, and V While in the idealized embodimentshown in FIG. 2 the overlapping produces two tiers of windings atvarious points about the core, in other instances desired magneticcharacteristics may be achieved by interleaving turns of the windings ina single tier so as to extend the effective lengths thereof withoutproducing a second, overlapping tier of windings. In either case,however, the magnetic flux enclosed by any two overlapping or adjacentturns of different windings is nearly identical.

It has been found that the overlapping or adjacent turns referred to maybe treated as unitary winding elements rather than as separate butcommingled horizontal and vertical winding turns. the overlapping oradjacent turns can therefore be electrically isolated and connectedtogether so as to form a new, separate winding. In FIG. 2, theinterleaved or overlapping turns of windings V, and H, are denominatedW, while the interleaved or overlapping turns of windings V, and H aredenominated W Similarly, interleaved or overlapping turns of windings Vand H, are denominated W, and those of windings V, and H, denominatedW,,. If the sets of turns denominated W,,, W,,, W and W, are removedfrom the core and replaced with four auxiliary windings formed from acontinuous length of conductor, a set of four series-connected windingsresult. After joining opposite ends of the conductor, the four windingsmay be considered to be in a bridge configuration.

Turning now to FIG. 3, a schematic drawing of the newly-achieved windingsystem is shown. The four new, auxiliary windings are series-connectedto form a closed loop and depicted as lying in a substantially squareconfiguration in the manner of a bridge. The now-shortened deflectionwindings serve to connect the bridge windings across suitable sources ofhorizontal and vertical deflection currents. One end of thenow-shortened vertical deflection winding denominated V, is coupled toone corner or node of the bridge at an intersection of two of the fournew, auxiliary windings. Similarly, one end of the other attenuatedvertical winding V is connected to a node at the opposite side of thebridge, at the intersection of the other two of the four new windings.

Each of the shortened horizontal deflection windings H, and H isconnected to one of the remaining nodes of the bridge. Thebridge-connected auxiliary winding whose ends are coupled to verticalwinding V, and

horizontal winding H, is denominated B,,, while that winding coupledbetween vertical winding V, and horizontal winding H is denominated B Inlike manner, the bridge winding lying between windings V and H, isdenoted B and that between windings V, and H denoted B All of thebridge-connected windings are thus in series circuit relationship withthe vertical and the horizontal deflection windings. Both the horizontaland the vertical deflection winding circuits thus have placed in seriestherewith two parallel sets of windings, each set consisting of a pairof series-connected windings.

If in the original yoke windings:

X the number of turns in each original horizontal winding H, and H and Ythe number of turns in each original vertical winding V, and V then 2Xthe total number of horizontal turns connected in series and 2Y thetotal number of vertical turns connected in series.

Now, if N the number of turns at the end of each winding which areadjacent to or overlap turns of an adjacent winding, after the deletionof these turns it will be understood that the yoke now will have X2Nturns per new horizontal winding H, and H and Y-2N turns per newvertical winding V, and V At each point where overlapping or adjacentturns of different windings have been removed, a new continuous windinghaving 2N turns is formed. Since at this location N turns have beendeleted from each of the original windings the 2N turns of the newwinding merely replace those deflection winding turns that have beeneliminated.

A total of four of the new or auxiliary windings are formed, and areconnected in a closed loop or bridge. Now, by coupling oppositejunctions or nodes formed between the bridge-connected windings inseries with horizontal windings H and H a new circuit element composedof 4N turns connected in parallel with 4N turns is interposed in thehorizontal deflection circuit.

If a constant R is taken to be the resistive multiplying factor in ohmsper turn of winding material, it will be seen that the originalhorizontal deflection windings had a resistance R,, of 2RX, while theoriginal vertical windings had a resitance R of 2RY. The inventivewinding circuit, now including the bridge-connected windings, willpresent both the resistance of the shortened deflection windings and theresistance arising across the bridge windings to the deflection currentsupply systems so that the total resistance R,,' arising across the newhorizontal deflection circuit is now 2R(XN) so that the resistance ofthe new horizontal deflection circuit is reduced by 2RN. Further, sincethe bridgeconnected windings are now interposed between the shortenedvertical deflection windings V and V it will be seen that the effectiveseries resistance R, of the vertical deflection circuit is now 2R(YN) sothat the total resistance of the vertical deflection circuit has alsobeen reduced by 2RN.

While the resistance across both the vertical and the horizontaldeflection circuits has been reduced, the magnetomotive force (mmf) ofboth circuits remains the same. Since magnetomotive force F is directlyproportional to the ampere-turns of a winding it may be considered thatthe mmf of the horizontal deflection circuit F,, is equal to the current1,, through the circuit times the number of turns, or

F 21,,X for the original horizontal circuit.

Each of the horizontal windings of the inventive circuit has had 2Nturns removed therefrom, and with the bridge windings connected betweenthe shortened horizontal windings H and H there are two paralleledwindings of 4N turns each added to the horizontal circuit. Assuming thathorizontal deflection current 1,, divides equally between both parallelbranches of the bridge-connected windings, recombining at the oppositeside of the bridge and flowing outwardly through the distal horizontaldeflection winding, the mmf F,,' of the horizontal deflection circuitwhen connected as shown in FIG. 3 may be represented as v n g so thatthe mmf and therefore the inductance of the new horizontal circuitincluding the bridge-connected windings is substantially the same asthat of the original deflection windings alone. Moreover, the spatialdistri' bution of the mmf giving rise to the magnetic flux about thewindings is substantially the same. It may easily be demonstrated thatthe above relationship also holds true for the new vertical deflectioncircuit shown in FIG. 3 so that the magnetic and inductivecharacteristics of the vertical deflection system are also unchanged.From the standpoint of the magnetic characteristics of the deflectionsystem the total number of effective turns in the inventive horizontaldeflection circuit is still 2X, and the total number of effective turnsin the vertical circuit is still 2). Hence, the total inductance of boththe horizontal and the vertical deflection circuits has not beenchanged. It can now be appreciated that, using the same amount ofconductor material as was utilized for a prior-art style yoke winding,the L-R ratio of the horizontal deflection circuit has been increased byl00(N/XN) per cent and the L-R ratio for the vertical deflection circuithas been increased by (N/Y-N) per cent.

The various bridge-connected auxiliary windings conduct differentialcurrents whose characteristics depend upon the relative phase andmagnitudes of vertical and horizontal deflection currents 1,, and l,,.Assuming current flow in the directions indicated in FIG. 3, it will beseen that currents 1,, and I, are additive in windings 8, and B andsubtractive in windings B and B The change in ampere-turns thus achievedcorresponds to the decrease in magnetic flux which would result fromopposing current flows in the interspersed turns W and W which thewindings B and B replace. Similarly, the increase in ampere-turns due tothe additive currents through windings B and B corresponds to theincreased flux which would result from the application of the individualdeflection currents to the separate, interspersed horizontal andvertical turns W and W,, at corresponding locations upon the yoke.

Damping means comprising capacitor 12 and resistor 13 are connected inseries between the input terminals of vertical winding V, and horizontalwinding H Similarly, the series combination of a capacitor 14 andresistor 15 are connected between the output terminals of verticalwinding V and horizontal winding H,'. The damping means serve tominimize ringing or oscillation which may be induced in the verticaldeflection windings due to the presence of higher-frequency signals inthe horizontal deflection windings. Of course, other circuitry may beadapted for the purpose and it will be appreciated that the series R-Ccircuits are shown for purposes of illustration, the bridge windingarrangement shown being amenable to various other damping arrangementsas required.

Alternatively, rather than increasing the L-R ratios of the respectivedeflection circuits the size of the conductor used for thebridge-connected windings may be reduced. A reduction in cross-sectionalarea of the conductor effects a corresponding increase in the resistancethereof, lowering the L-R ratio but saving conductor material. ForinstanceTifthe'fiV'turns'of wire per bridge winding are constructed ofwire having onehalf the cross-sectional area of the wire used forwinding's V V2, H1, and Hz. the inductance of the resulting deflectioncircuits will be substantially the same as that of the originalcircuits; but since the resistivity of the bridge circuit is doubled theoverall series resistance of the horizontal and vertical deflectioncircuits will match that of the original, prior-art yoke windingconfiguration.

It will therefore be seen that it is advantageous to use as manybridge-connected turns as possible in a given deflection systemconfiguration. In the ultimate it may be desirable to use onlybridge-connected windings, re-

ducing the number of peculiarly horizontal and vertical winding turns tozero. In general, however, the required winding distributions militateagainst this approach.

One winding distribution which is considered optimal for a toroidal yokeused in conjunction with color television receiver cathode ray tubes inwhich three electron beams disposed in a planar array are deflected overa maximum included angle of 70 is shown in FIG. 4. This embodimentincorporates an economic advantage in that it may be constructed bycontinuous winding of conductor material about the core, while includingan interleaving and overlapping of windings which provides the desiredwinding distribution.

FIG. 4 shows a composite winding distribution upon the developed surfaceof one quadrant of an annular core, which includes one half ofhorizontal winding H bridge winding B and one half of vertical winding VIt is assumed that the turns are deposited on the core by winding fromright to left, the start of each winding being denoted by S and thefinish or final turn by F.

The winding distributions on adjacent yoke quadrants being symmetrical,it will be understood that the major part of winding H, is disposed in acontinuous fashion for approximately 22 slots on either side of a pointdenominated on the yoke core with a small, discontinuous group of turnsdisplaced substantially four slots from either end thereof. Similarly,the bridgeconnected auxiliary windings B and B are orientedsymmetrically about the 0 position and extend in a continuous manner oneither side thereof for 35 slots, resuming after a hiatus of four slotsand extending again for substantially 12 slots.

The vertical deflection windings V, and V are disposed about the 90 and270 positions upon the core, respectively. They are distributedoutwardly therefrom and so bracket the 0 position in a symmetricalfashion. FIG. 4 shows the right-hand half of vertical winding V it beingconsidered unnecessary to illustrate the entire winding due to itssymmetrical nature. The turns extend in a continuous fashion forapproximately 14 slots about the 90 position, and then in three separatesets of eight, five, and four turns spaced outwardly from the ends ofthe central winding segment by substantially five, l5, and 26 slotsrespectively.

It is evident that while the bridge-connected windings are disposed inboth a first and a second tier, the bridge windings actually occupy onlya single layer at any point upon the core surface. Similarly, both thevertical and the horizontal windings comprise single layers, eachremaining in a single tier. This winding configuration lends itself toease of manufacture, since the various windings may be disposed upon atoroidal yoke by progressively winding in a common direction about thetoroid, with no need of backing up" to deposit a second layer ofwindings. Vertical windings V, and V are deposited first, and then thevarious bridge windings are formed on the core. Finally, the horizontalwindings H, and H are disposed in a second tier over the bridge windingsand the vertical deflection windings.

Of course, facility of disposition of the windings upon a core issecondary to the proper distribution of the deflection winding turns. Asused herein, the term winding distribution indicates the overallmagnetic effect produced by a group of inter-related turns, rather thanthe discrete positioning of the turns thereof. In calculating theeffective winding distribution, bridgeconnected winding turns areassigned a value one-half that of the turns within exclusivelyhorizontal or vertical deflection windings. As explained above, it isconsidered that each bridge-connected winding conducts one-half of thehorizontal deflection current and onehalf of the vertical deflectioncurrent.

Referring now to FIG. 5, the effective winding distribution in theoverall horizontal circuit of FIG. 4, including the bridge-connectedwindings appended thereto, is shown. The vertical axis represents theprecentage of the total turns extending from the geometric center of thewinding to the distal end thereof. The horizontal axis representsangular position on the yoke, it being recognized that the actual numberof slots or turn positions varies with conductor size and the diameterof the core means. The distribution of FIG. 5 thus may be used tocharacterize physically different windings which have similarmagnetomotive characteristics, regardless of the actual number of turnsor the diameter of the core means.

Similarly, FIG. 6 represents the effective vertical deflection windingdistribution from the geometric center to one extremity thereof,including bridge-connected winding B which lies in the illustrated yokequadrant and contributes to the overall vertical winding distribution.As set forth above, the winding distribution shown, while illustrativeof the actual turn placement set forth in FIG. 4, may be consideredcharacteristic of the geometric winding type which produces the desiredmagnetic flux characteristic.

As will be recognized by those skilled in the art, a two-dimensionalconfiguration such as a waveform, or a spatial distribution such as theturns placement shown in FIG. 4, may be considered to be constituted byan infinite series of sinusoidal functions whose frequencies areintegral multiples of a fundamental frequency. Where the frequencymultiplier is greater than one, the function is termed a harmonic. Sucha series, known as a Fourier series, may be represented in a form A sin4; B sin (34 C sin (Sqb) D sin (7(1)) E Due to the symmetry of thepresent winding distribution even-numbered harmonics, i.e. those havingevennumbered frequency multipliers, are not present. A Fourier analysisof the overall horizontal deflection winding distribution of FIG. 4including the bridge winding turns, which are assigned a value one-halfthat of horizontal winding turns, reveals that the coefficient of thethird harmonic (B) is substantially greater than those of other, higherorder harmonics. On a normalized scale wherein the coefficient A of thefundamental is taken as 1, the coefficients calculated for the instantwinding distribution are normalized fundamental and the above thirdharmonic value.

The overall vertical deflection winding distribution, which reflects theeffectivevalue of the bridge windings, produces a Fourier series thecoefficients of which have absolute values somewhat similar to those ofthe horizontal distribution. On a normalized scale, the coefficientscalculated for the vertical winding distribution of FIG. 4 areCami-none;

so that again, the third harmonic is much larger than higher-orderharmonics. I-lere also, analysis has shown that the effectivedistribution illustrated in FIG. 6 may be substantially reproduced fromthe fundamental and the third harmonic.

The winding distribution thus characterized, in addition to facilitatingthe disposition of the various turns upon a core, produces magneticfields well adapted for the deflection of electron beams in a colorcathode ray tube of the type in which three electron beams are disposedin a planar array. It is contemplated that other, equivalentcombinations of winding turn placements may be utilized to produceeffective distribution shown.

A turns location arrangement utilizing bridgeconnected windings which ispresently preferred for a toroidal yoke used in conjunction with a colorcathode ray tube of a type in which three electron beams disposed in atriangular or delta array are deflected over a maximum included angle of90 is shown in FIG. 7. As was the case in FIG. 4, the symmetry of thetoroidal winding allows the entire turns placement scheme to becharacterized by one quadrant thereof. As before, the position on thedeveloped core corresponds to the midpoint of the right-hand side of theidealized yoke represented in FIG. 2. Horizontal deflection winding H,is thus centered about the 0 position, while vertical deflection windingV, is centered about the 90 point.

FIGS. 8 and 9 show the cumulative percentage of the total effectiveturns from the center of each winding to the distal end thereof,including the associated bridgeconnected winding. The solid curve ofFIG. 8 represents the cumulative number of effective turns, assigningeach turn of a bridge-connected winding one-half the value of a turn ofthe peculiarly horizontal winding. The winding distribution shown inFIG. 8 therefore incorporates the effective turns of both one half ofhorizontal winding H and the bridgeconnected auxiliary winding B itbeing realized that the same bridge winding also contributes to thevertical winding distribution. It will be understood that the effectivehorizontal turns actually extend for somewhat less than 180 upon theyoke, the dotted portions of the curve which extend illustrating thecharacteristics of a modified winding distribution to be discussedbelow.

As was the case for the winding distribution whose turns placement wasillustrated in FIG. 4, the present horizontal winding distribution maybe characterized by a Fourier series of the form A sin 0 B sin (36) Csin (50) D sin (76) E sin ()+Fsin ()+G sin (I36)+. .Onanormalized scale,the coefficients calculated for the horizontal winding distribution ofFIG. 7 are:

so that all of the harmonics are very small with respect to thefundamental. It can be demonstrated that the effective horizontalwinding distribution of FIG. 8 can be substantially reconstructedutilizing only the fundamental, the equivalent of a substantiallysinusoidal distribution.

FIG. 9 is a plot of a preferred vertical winding distri bution. In FIG.9, the vertical axis represents the percentage of the total number ofeffective turns from the center of the winding to the outer end thereof,while the horizontal axis corresponds the developed length of a quadrantof the inner surface of an annular core upon which the windings aredisposed. As explained with reference to FIG. 8, turns of bridgewindings associated with the vertical windings of interest are eachassigned one-half the value of an exclusively vertical winding turn,since the vertical deflection current which is carried by the bridgewindings is one-half that carried by the vertical deflection windingitself.'A Fourier analysis of the effective vertical windingdistribution shows that, in contradistinction to the effectivehorizontal winding distribution of FIG. 5, the fifth harmoniccoefficient (C) is not insignificant. The distribution represented inFIG. 9 may therefore be approximated by a Fourier series of the typeindicated above wherein the normalized coefficients are o-nmunw Whilethe set of Fourier coefficients listed above describes the windingdistribution to a high degree of accuracy, it has been found that awinding distribution reconstructed from the fundamental, third and fifthorder harmonics substantially duplicates the desired effectivedistribution. The described winding distribution has been found to havecharacteristics which are highly desirable for use in a toroidal yoke inconjunction with a color television cathode ray tube of the type whereinthree electron beams disposed in a triangular or delta array aredeflected through a maximum included angle of 90.

Turning now to FIG. 10 there is shown still another form ofbridge-connected winding, which produces different fluxes for similarhorizontal and vertical currents applied thereto. As before, the varioushorizontal and vertical deflection windings are connected to opposingcorners of other, auxiliary windings which in turn are connected in abridge configuration. In FIG. 10, however, certain turns of each bridgewinding have been interchanged with corresponding turns from an adjacentwinding. Bridge winding B for instance, comprises a first segment P anda second segment p while bridge winding B which also receives currentfrom horizontal winding H comprises first and second segments Q and qrespectively. Bridge winding B which is connected to horizontal windingH comprises a first segment S and a second segment 5 while the otherbridge winding B connected to horizontal winding H comprises first andsecond segments T and 2, respectively. For purposes of illustration, itwill be assumed that all of the first segments of each bridge windingcontain like numbers of turns, as do all of the second segments so thatthe turns comprising the second segments of each bridge winding may beinterchanged with those of an adjacent bridge winding. The turns whichcomprise winding segment q are interchanged with those of segment p, andthe turns of segment s are interchanged with those constituting segmentt. By proper connection of the interchanged winding segments a circuitlike that schematically represented in FIG. is obtained.

The direction of vertical deflection current I, is indicated by solidarrows, and the direction of horizontal deflection current I, by dashedarrows. Assuming that the turns of all bridge-connected windings arewound about the core in a common direction, it follows that adjacentwinding segments which carry like-directed current will producelike-directed magnetic flux. Similarly, winding segments in whichcurrents flow in opposite directions produce oppositely-directed fluxes.For example, the vertical deflection current 1,, in first windingsegment P of bridge winding B is directed in a manner similar to that ofsecond winding segment q which is adjacent thereto. However, horizontaldeflection current I,,, whose direction is indicated by the dottedarrows, flows through the first winding segment P in a directionopposite to that through second winding segment q.

The magnetic flux supported by the various bridge windings is increasedby additive currents in the first and second portions thereof, anddecreased by subtractive or differential currents. In the presentinstance the vertical deflection characteristics, and therefore theeffective vertical winding distribution, remain unchanged despite thealtered bridge winding configuration. In contrast the horizontal windingdistribution, and therefore the deflection characteristics resultingtherefrom, is substantially modified. Each bridge-connected winding maynow be considered to consist of a first winding segment derived from theoriginal winding and a second winding segment borrowed from itsneighbor. If there are 2n turns in each of the second winding segmentsp, q, s, and t and 2N turns in each original bridge-connected auxiliarywindings so that the first winding segments each comprise 2(Nn) turns,the mmf produced by vertical current I,,/2 flowing in anybridge-connected winding will be I,,N while the flux produced byhorizontal current I,,/2 flowing therethrough will be 1,,(N-2n). Theinductance presented to the vertical deflection system will thus remainunchanged, while the inductance presented to the horizontal deflectionsystem will be reduced. The winding configuration shown in FIG. 10 thusprovides a modified distribution for one of the deflection windingcircuits at the expense of a somewhat lessened L-R ratio.

Referring now to FIG. 7a, there is shown a portion of the developedtoroidal core quadrant represented in FIG. 7, with windings representedthereon in cross section. FIG. 7a shows only ehe windings disposed atone side of the juncture of the two quadrants which form the upper halfof a toroidal yoke of the type illustrated in FIG. 2, wherein theright-hand extremity is taken to be 0 and top dead center is The 90position is located at the rightward end of the developed view shown inthe Figure. In the distribution of FIG. 7, bridge winding B begins atslot 60 (approximately 82) and is wound in a progressive clockwisefashion to slot 3 which is located at approximately 4 on the core, theinitiation or starting point of the bridge winding being denominated S8and the end or finish FB Vertical winding V is disposed in a second tierover winding B for the first 42 of the bridge-connected winding. Thevertical windings are disposed in the unoccupied first tier between the82 and 90 points or between the initial turn of bridge winding B to thefinal turn of bridge winding B In order to produce the necessary windingdistribution, however, a single tier of vertical windings between 82 and98? (slots 61 through 72) is inadequate. For this reason, sevenadditional vertical winding turns are disposed in a second tier inaltemating positions. It will now be seen that there are a total of nineeffective vertical turns lying in slots 67-72 of the second quadrant.

FIG. 7a shows in developed form the rightward end of the yoke quadrantshown in FIG. 7. In order to optimize the use of the bridge windings andincrease the L-R ratio of the vertical windings, some of the verticalwinding turns which had originally been disposed in slots 61-66 havebeen deleted and certain bridgeconnected winding turns have been added.The turns placement and connection gives rise to an asymmetrical mmfcontribution from the bridge windings to produce an effective windingdistribution which is substantially identical to that of FIG. 7 for thevertical windings, and nearly so for the horizontal windings.

It will be recalled that the bridge windings as disclosed abovenecessarily carry both horizontal and vertical deflection currentTherefore, in providing bridgeconnected winding turns of the typeheretofore described it would be necessary to accept horizontal fluxcomponents over the length of the entire bridgeconnected winding. Itwould in some cases be detrimental to the deflection characteristicsdesired, however, if such horizontal components were to appear in thearea about the 90 point of the yoke.

The distribution of the turns of the bridge-connected windings shown inFIG. 7a provides the advantages which inhere in the bridge windingconfiguration to the vertical deflection circuit without introducingunwanted magnetic flux arising from the horizontal deflection signals.In FIG. 7a bridge winding B and B are each extended by a total of sixturns to replace the first tier of vertical deflection windings lying inslots 61-66 and 67-72, respectively; and three vertical winding turnsare added to the second winding tier. Since each bridge winding turn hasonly one half the effective value of a corresponding vertical windingturn, the six vertical turns and six bridge turns equalnine effectivevertical turns, the same number as had originally been disposed in slots60-66. Since the windings are symmetrically distributed about the 90position, the effect is the same for turns of winding B in slots 67-72.The mere provision of bridge winding turns, however, will still supporthorizontal flux components, as set forth above.

To cancel the effect of horizontal current in certain bridge windingturns, the winding connection shown in FIG. is utilized. The first turnof bridge winding B is placed in slot 72, the winding progressing in aclockwise fashion about the core, herein corresponding to a leftwarddirection. A total of three turns of bridge winding B are interchangedwith three turns of adjacent bridge winding B In the presentillustration, turns of winding B lying in slots 61, 62, and 66 areremoved, and the three turns thus eliminated are placed in slot 67, 71and 72 and so are interspersed with turns of bridge winding B The turnsof bridge winding B thus displaced are now substituted for those deletedfrom winding B in slots 61, 62, and 66. While the illustrated bridgewindings are wound in a common direction, the interchanged windingscarry horizontal deflection current which flow in opposing directions.When vertical deflection current is applied to the bridge windings,additive fluxes will be produced in the same manner as if the windingturns had never been interchanged. The effective vertical windingdistribution thus remains unchanged.

For horizontal deflection current, however, fluxes are produced by eachbridge winding which buck those produced about the interchanged turnssuch that the interchanged turns effectively cancel the adjacent,original bridge windin turns to produce a subtractive effect and thusnullify the horizontal deflection flux in portions of the regionillustrated. The turns of winding B which extend into the secondquadrant and are interspersed with those of winding B, correspond to thesecond winding segment q of FIG. 10. Similarly, turns of winding B whichextend into the first quadrant symmetrically with segment q of winding Bcorrespond to segment p of FIG. 10.

In the example illustrated in FIG. 7, a total of 59' tur n s areprovided in each of the vertical windings with 50 turns in each bridgewinding. The horizontal windings each have a total of 64 turns therein.It will be under stoo d thatthe induc mce L presented to the verticaldeflection drive system is then due to 218 turns while the inductance Lpresented to the horizontal system is attributable to 228 turns Theresistance R of the overall vertical winding system is 2R (59 50/2) or168 R ohms while the horizontal resistance R,, is

2R (64 50/2)- or 178 R ohms.

For the improved circuit of FIG. 7a, the inductance of the aggregateeffective vertical turns is due to 2(53 56) 218 turns while horizontalinductance is due to the presence of 2(64 53 3) 228 turns.

While the inductance of the horizontal and the vertical effectivewinding distribution is substantially the same, the presence ofadditional bridge-connected winding turns reduces the resistance of theoverall vertical winding system to l62 R ohms while that of thehorizontal system is now 184 R ohms.

The illustrated modification in turns placement makes it possible toreduce the vertical deflection winding turns to a single layer so thatthe turns may be wound in a continuous, progressive manner without theneed to back up to deposit a second layer of turns.

The effect of the modified turns placement shown in FIG. 7a may be seenin the plot of effective horizontal winding distribution of FIG. 3. Forclarity the terminal portion of the curve is shown in expanded form. Thedotted portion of the curve extending for the last 8 of the quadrant(here equivalent to six slots or turn positions) represents the effectof the additional bridgeconnected winding turns. The percent ofeffective winding, measured from the center of the horizontal winding,decreases for slots 61-62, reflecting the presence of the turnsinterposed from bridge winding B The percentage of total winding thenincreases for the following three slots due to the presence of theadditional turns of bridge winding B in slots 63-65. The distributionthen decreases by one slot due to the presence of theoppositely-directed current in the final turn of the quadrant. The threeadditional turns of bridge winding B have thus been nulled by thepresence of the three counter-wound turns borrowed from winding B sothat the total percentage of windings from center has not been affected.As described above, for the vertical effective winding distribution nineeffective turns continue to be present in slots 61-66 such that there isno demonstrable change in the effective vertical winding distributionplotted in FIG. 9.

As will be evident from the foregoing description, certain aspects ofthe invention are not limited to the particular details of the examplesillustrated, and it is therefore contemplated that other modificationsor applications will occur to those skilled in the art. For instance,the number of turns in a given bridge winding is not necessarily an evennumber, and the grouping of interspersed ones of turns of adjacentbridge windings may be varied to suit a particular application. It isaccordingly intended that the appended claims shall cover all suchmodifications and applications as do not depart from the true spirit andscope of the invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. Means for effecting the periodic deflection of an electron beamwithin a cathode ray tube, comprising:

core means adapted to be disposed about the neck of the cathode raytube;

a first pair of windings disposed on said core means for deflecting theelectron beams in a first direction;

a second pair of windings disposed on said core means for deflecting theelectron beam in a second direction substantially perpendicular to thefirst direction;

first, second, third, and fourth windings disposed on said core meansand connected in series relationship with one another to form a closedloop, said first and said second windings each having at least one turndisposed intermediate the ends of the other;

said third and said fourth windings each having at least one turndisposed intermediate the ends of the other;

means for coupling the junction of said first and said second, and thejunction of said third and fourth, windings in series circuitrelationship with said first pair of windings across a first source ofdeflection signals; and

means for coupling the junction of said second and third, and thejunction of said fourth and first, windings in series circuitrelationship with said second pair of windings across a second source ofdeflection signals.

2. The invention defined in claim 1, wherein said turns disposedintermediate the ends of another winding are disposed upon the coremeans in such a manner that deflection signals from the second sourceproduce magnetic flux which aids, and deflection signals from the firstsource produce magnetic flux which opposes, the flux produced by thewinding intermediate whose ends said turns are disposed.

3. The invention defined in claim 1, wherein said first pair of windingsis adapted to deflect the electron beams in a horizontal direction, andsaid second pair of windings is adapted to deflect the electron beams ina vertical direction.

4. In a color television receiver including a cathode ray tube havingelectron gun means adapted to produce a plurality of electron beams,means for periodically deflecting the electron beams, comprising:

annular core means adapted to be disposed about the neck of the cathoderay tube;

a first pair of windings associated with said core means for deflectingthe electron beams in a direction perpendicular to a given plane;

a second pair of windings associated with said core means for deflectingthe electron beams in a direction substantially parallel to said givenplane;

first, second, third, and fourth windings disposed on said core meansconnected in series relationship with one another to form a closed loop,each of said first, second, third, and fourth windings comprising afirst and a second segment;

the second segments of said first and second windings being disposed onsaid core means intermediate the first and second segments of the other;

the second segments of said third and fourth windings being disposed onsaid core means intermediate the first and second segments of the other;

means for coupling the junctions of said first and said second, andthird and said fourth, windings in series circuit relationship with saidfirst pair of windings across a first source of deflection signals; and

means for coupling the junctions of said second and third, and saidfourth and first, windings in series circuit relationship with saidsecond pair of windings across a second source of deflection signals.

5. The invention defined in claim 4, wherein said second segments ofsaid windings are disposed on said core means in such a manner thatdeflection current from the second source of deflection signals producesmagnetic fluxes about the second segments which aid, and deflectioncurrent from the first source of deflection signals produces magneticfluxes about the second segments which oppose, the fluxes produced bythe winding intermediate whose segments they are disposed.

6. In a television receiver containing deflection apparatus fordeflecting the electron beams of the cathode ray tube, said deflectionapparatus including a core for receiving the neck portion of saidcathode ray tube and horizontal and vertical windings wound on saidcore, wherein proper deflection of said electron beams requiressufiieient windings such that adjacent horizontal and vertical windingsare ordinarily caused to overlap, the improvement comprising:

first, second, third and fourth auxiliary windings wound on said core,each of said auxiliary windings having turns proportional to the numberof overlapped turns between adjacent horizontal and vertical windings,

each auxiliary winding replacing the overlapped portion of each ofadjacent horizontal and vertical windings such that shortened horizontaland vertical windings are utilized,

said auxiliary windings being serially interconnected to form a closedloop,

said shortened horizontal windings connecting selected alternatejunctions of said auxiliary windings to a source of horizontaldeflection signals,

and said shortened vertical windings connecting the other junctions ofsaid auxiliary windings to a source of vertical deflection signals.

7. The improved deflection apparatus recited in claim 6 wherein saidhorizontal and vertical windings each contain a pair of windings,

one of said shortened horizontal windings being connected to thejunction between the first and second auxiliary windings, the other ofsaid shortened horizontal windings being connected to the junctionbetween said third and fourth auxiliary windings, one of said shortenedvertical windings being connected to the junction between said secondand third auxiliary windings, the other of said shortened verticalwindings being connected to the junction between said fourth and firstauxiliary windings.

8. In a television receiver deflection apparatus for deflecting theelectron beams in the cathode ray tube comprising:

a core for receiving the neck portion of said cathode ray tube,

horizontal windings, vertical windings and first, second, third andfourth auxiliary windings contiguously wound on said core,

said first, second, third and fourth auxiliary windings being seriallyinterconnected to form a closed loop,

said horizontal windings connecting the junctions between said first andsecond and third and fourth auxiliary windings to a source of horizontaldeflection signals to form a series connection between said horizontalwindings, the source of horizontal signals and said auxiliary windings,

said vertical windings connecting the junctions between said second andthird and fourth and first auxiliary windings to a source of verticaldeflection signals to form a series connection between said verticalwindings, the source of vertical signals and said auxiliary windings.

9. The deflection apparatus recited in claim 8 wherein said horizontalwindings comprise first and second windings,

the first horizontal winding connecting the junction between said firstand second auxiliary windings to the source of horizontal signals, thesecond horizontal winding connecting the junction between said third andfourth auxiliary windings to the source of horizontal signals,

and said vertical windings comprise first and secone windings,

the first vertical winding connecting the junction between said secondand third auxiliary windings to the source of vertical signals, thesecond vertical winding connecting the junction between said fourth andfirst auxiliary windings to the source of vertical signals. j

10. The deflection apparatus as recited in claim 8 wherein saidhorizontal windings and said auxiliary windings comprise a first set ofwindings disposed about a first pair of diametrically opposite points onsaid core and being arranged about each of said points to provide aneffective winding distribution substantially characterized by sin 0.08sin(3) where qb represents the angular displacement from the geometriccenter of the winding,

and said vertical windings and said auxiliary windings comprise a secondset of windings disposed about a second pair of diametrically oppositepoints on said core displaced substantially from the first points andbeing arranged about each of said second points to provide an effectivewinding distribution substantially characterized by sind: 0.06 sin(3).

11. The invention defined in claim 5 wherein said first pair of windingsand said first, second, third and fourth windings comprise a first setof windings disposed about a first pair of diametrically opposite pointson said core and being arranged about each of said points to provide aneffective winding distribution of substantially sinusoidal form,

and said second pair of windings and said first, second, third andfourth windings comprise a second set of windings disposed about asecond pair of diametrically opposite points on said core displacedsubstantially 90 from the first points and being arranged about each ofsaid second points to provide an effective winding distributionsubstantially characterized by sin 0.04 sin(3) 0.016 sin(5) where 5represents the angular displacement from the geometric center of thewinding.

1. Means for effecting the periodic deflection of an electron beamwithin a cathode ray tube, comprising: core means adapted to be disposedabout the neck of the cathode ray tube; a first pair of windingsdisposed on said core means for deflecting the electron beams in a firstdirection; a second pair of windings disposed on said core means fordeflecting the electron beam in a second direction substantiallyperpendicular to the first direction; first, second, third, and fourthwindings disposed on said core means and connected in seriesrelationship with one another to form a closed loop, said first and saidsecond windings each having at least one turn disposed intermediate theends of the other; said third and said fourth windings each having atleast one turn disposed intermediate the ends of the other; means forcoupling the junction of said first and said second, and the junction ofsaid third and fourth, windings in series circuit relationship with saidfirst pair of windings across a first source of deflection signals; andmeans for coupling the junction of said second and third, and thejunction of said fourth and first, windings in series circuitrelationship with said second pair of windings across a second source ofdeflection signals.
 2. The invention defined in claim 1, wherein saidturns disposed intermediate the ends of another winding are disposedupon the core means in such a manner that deflection signals from thesecond source produce magnetic flux which aids, and deflection signalsfrom the first source produce magnetic flux which opposes, the fluxproduced by the winding intermediate whose ends said turns are disposed.3. The invention defined in claim 1, wherein said first pair of windingsis adapted to deflect the electron beams in a horizontal direction, andsaid second pair of windings is adapted to deFlect the electron beams ina vertical direction.
 4. In a color television receiver including acathode ray tube having electron gun means adapted to produce aplurality of electron beams, means for periodically deflecting theelectron beams, comprising: annular core means adapted to be disposedabout the neck of the cathode ray tube; a first pair of windingsassociated with said core means for deflecting the electron beams in adirection perpendicular to a given plane; a second pair of windingsassociated with said core means for deflecting the electron beams in adirection substantially parallel to said given plane; first, second,third, and fourth windings disposed on said core means connected inseries relationship with one another to form a closed loop, each of saidfirst, second, third, and fourth windings comprising a first and asecond segment; the second segments of said first and second windingsbeing disposed on said core means intermediate the first and secondsegments of the other; the second segments of said third and fourthwindings being disposed on said core means intermediate the first andsecond segments of the other; means for coupling the junctions of saidfirst and said second, and third and said fourth, windings in seriescircuit relationship with said first pair of windings across a firstsource of deflection signals; and means for coupling the junctions ofsaid second and third, and said fourth and first, windings in seriescircuit relationship with said second pair of windings across a secondsource of deflection signals.
 5. The invention defined in claim 4,wherein said second segments of said windings are disposed on said coremeans in such a manner that deflection current from the second source ofdeflection signals produces magnetic fluxes about the second segmentswhich aid, and deflection current from the first source of deflectionsignals produces magnetic fluxes about the second segments which oppose,the fluxes produced by the winding intermediate whose segments they aredisposed.
 6. In a television receiver containing deflection apparatusfor deflecting the electron beams of the cathode ray tube, saiddeflection apparatus including a core for receiving the neck portion ofsaid cathode ray tube and horizontal and vertical windings wound on saidcore, wherein proper deflection of said electron beams requiressufficient windings such that adjacent horizontal and vertical windingsare ordinarily caused to overlap, the improvement comprising: first,second, third and fourth auxiliary windings wound on said core, each ofsaid auxiliary windings having turns proportional to the number ofoverlapped turns between adjacent horizontal and vertical windings, eachauxiliary winding replacing the overlapped portion of each of adjacenthorizontal and vertical windings such that shortened horizontal andvertical windings are utilized, said auxiliary windings being seriallyinterconnected to form a closed loop, said shortened horizontal windingsconnecting selected alternate junctions of said auxiliary windings to asource of horizontal deflection signals, and said shortened verticalwindings connecting the other junctions of said auxiliary windings to asource of vertical deflection signals.
 7. The improved deflectionapparatus recited in claim 6 wherein said horizontal and verticalwindings each contain a pair of windings, one of said shortenedhorizontal windings being connected to the junction between the firstand second auxiliary windings, the other of said shortened horizontalwindings being connected to the junction between said third and fourthauxiliary windings, one of said shortened vertical windings beingconnected to the junction between said second and third auxiliarywindings, the other of said shortened vertical windings being connectedto the junction between said fourth and first auxiliary windings.
 8. Ina television receiver deflection apparatus For deflecting the electronbeams in the cathode ray tube comprising: a core for receiving the neckportion of said cathode ray tube, horizontal windings, vertical windingsand first, second, third and fourth auxiliary windings contiguouslywound on said core, said first, second, third and fourth auxiliarywindings being serially interconnected to form a closed loop, saidhorizontal windings connecting the junctions between said first andsecond and third and fourth auxiliary windings to a source of horizontaldeflection signals to form a series connection between said horizontalwindings, the source of horizontal signals and said auxiliary windings,said vertical windings connecting the junctions between said second andthird and fourth and first auxiliary windings to a source of verticaldeflection signals to form a series connection between said verticalwindings, the source of vertical signals and said auxiliary windings. 9.The deflection apparatus recited in claim 8 wherein said horizontalwindings comprise first and second windings, the first horizontalwinding connecting the junction between said first and second auxiliarywindings to the source of horizontal signals, the second horizontalwinding connecting the junction between said third and fourth auxiliarywindings to the source of horizontal signals, and said vertical windingscomprise first and secone windings, the first vertical windingconnecting the junction between said second and third auxiliary windingsto the source of vertical signals, the second vertical windingconnecting the junction between said fourth and first auxiliary windingsto the source of vertical signals.
 10. The deflection apparatus asrecited in claim 8 wherein said horizontal windings and said auxiliarywindings comprise a first set of windings disposed about a first pair ofdiametrically opposite points on said core and being arranged about eachof said points to provide an effective winding distributionsubstantially characterized by sin phi + 0.08 sin(3 phi ) where phirepresents the angular displacement from the geometric center of thewinding, and said vertical windings and said auxiliary windings comprisea second set of windings disposed about a second pair of diametricallyopposite points on said core displaced substantially 90* from the firstpoints and being arranged about each of said second points to provide aneffective winding distribution substantially characterized by sin phi-0.06 sin(3 phi ).
 11. The invention defined in claim 5 wherein saidfirst pair of windings and said first, second, third and fourth windingscomprise a first set of windings disposed about a first pair ofdiametrically opposite points on said core and being arranged about eachof said points to provide an effective winding distribution ofsubstantially sinusoidal form, and said second pair of windings and saidfirst, second, third and fourth windings comprise a second set ofwindings disposed about a second pair of diametrically opposite pointson said core displaced substantially 90* from the first points and beingarranged about each of said second points to provide an effectivewinding distribution substantially characterized by sin phi + 0.04 sin(3phi ) + 0.016 sin(5 phi ) where phi represents the angular displacementfrom the geometric center of the winding.